Hygrometer



Sept. 24, 1935 H. s. POLIN 2,015,125

HYGROMETER Filed Jan. 11, 1934 INVENTOR HERBERT 5. POZ/A/ ATTORNEYj Patented- Sept. 24, 1935 HYGROMET-ER Herbert Spencer Polin,

Island, N. Y., a corporation Port Washington, Long N. Y., asaignor to Polin, Inc New York,

of Delaware 4 Application January 11, m4. Serial No. 'maaoc comm. (01. -183) This invention. relates to hygrometric measurements, and particularly to electrical apparatus and method of using it, whereby the moisture content of gases may be readily and continuously determined.

Heretofore, certain electrical hygrometers have utilized spaced conductors connected by porous hygroscopic material. This porous material, on being exposed to an atmosphere containing moisture, becomes impregnated with water, thus being rendered conductive. The amount of moisture absorbed and hence the conductivity, is dependent upon the moisture content of the atmosphere. The resulting variations in the electrical resistance of the porous material have been used to affect electrical measuring devices. Such hygrometers are of little value in certain fields because an objectionable time lag is introduced, due to the fact that moisture, once absorbed by the porous material, is not readily evaporated, as the moisture is held interiorly, and the process of evaporation of this moisture is necessarily slow.

Other types .of electrical hygrometers have utilized closely spaced conductors embedded in a web of glass wool, which serves as an hygroscopic material, by deposit of moisture on the surface of this glass wool, rendering the surface thereof conducting. Hereagain an objectionable time lag occurs, as there are numerous interstices and cells between the filaments oi the glass wool which prevent a free circulation of the surrounding gas past the hygroscopic surfaces, which tend to prevent free evaporation and deposition of water.

The object of my invention is to provide an electrical hygrometer which is free from these defects, and is instantly responsive to any changes in moisture content of the atmosphere in which it is placed.

I have discovered that if I place a simple surface, without porosities or irregularities, such as the surface of a ceramic or glass cylinder, in an humid atmosphere which is in a state of flux with respect to the surface, a film of moisture is deposited on the surface which depends on the moisture content of the atmosphere. Thus the surface is rendered conducting. The amount of moisture deposited on the surface, and hence its conductivity varies with the moisture content of the atmosphere.

In my device, as I use it, there is no time lag, as the humid gas is constantly flowing past the surface of the electrode, and the accumulation of moisture is constantly evaporating and being redeposited. This use of fluent atmosphere is extremely important, as without it the air around the electrode becomes static and the moisture accumulation on the surface ceases to follow precisely the moisture content of the atmosphere. Unless a flow of the gas past the electrode is 6 maintained, even the plain surface of my device fails to respond rapidly to changes in humidity, and becomes inactive. The atmosphere may be made to fiow past the hygroscopic surface, as by blowing it, or the device may be placed on a 10 moving vehicle v In one embodimentof the device I use a simple glass tube, with two metal electrodes, placed diametrically opposite, protruding into the interior. A vacuum pump, fan, or other suitable 15 device is then used to force the atmosphere ,through the cylinder, and the interior surface thereof is used as the hygrwcopic surface. It is, of course, obvious that instead of forcing the gas through the cylinder, the electrode could be 20 fastened on to a moving vehicle, as the wing of an airplane, to cause the atmosphere to move with respect to it. Identified with the electrodes is a source of electrical energy and a resistance, and variations in the resistance of the hygroscopic 25 surface are used to cause variations in the current flow in this circuit. These efiects are amplifled by means of a thermionic device for providing a suitable indication thereof.

The single figure of thedrawlng shows dia- 30 grammatically a preferred embodiment of my invention.

The electrode device D consists of a section of glass tubing I, supporting opposed, interiorly protruding electrodes 2, preferably of platinum. These are series connected by conductors 3 with a source of voltage B1, a resistance R1 and the grid-cathode path of a thermionic tube V. The source B1 is poled to produce a positive bias on the grid G1 of tube V. Cathode K of tube V is energized by source B2, which also serves to energize the anode-cathode path of the tube. Anode A of tube V is connected to one extremity of a potentiometer R2, R3, R4, the other extremity of which is variably tapped through resistance R5 to a potentiometer Re, the fixed arm of which is bridged in shunt to battery B2. An indicating device M is connected in shunt with potentiometer 1 R2. R3, R4.

Grid (3; is negatively biased by means of battery B; the positive side of which is connected to the negative side of source B2. The biasing battery B3 is shunted by a potentiometer R1 variably tapped through a leak resistor Ra to the control grid G1, for providing an adjustable bias. Screen 55 battery Ba. k

The grid leak desistance Re is very serves to prevent the grid from becoming free" or floating, i. e. it serves to prevent accumulation of free charges on the grid 6, should the electrode device Dbecome so dry as to become a substantially perfect insulator.

Cathode K is variably tapped by connection 4 to the potentiometer Ra. By proper adjustment of tap 4 to potentiometer R: as well as the-tap to potentiometer Re, the extremities 5 and 6 of the potentiometer R2, R3, R4, maybe brought to the same potential for a selected reference condition of device D, providing thereby a zero reference indication on meter M.

A ian'F or other suitable device may be'employed to induce a continuous flow of the gas through device D. 0r such flow may be obtained by mounting device D on a member, such as an airplane wing, movable with respect to the gas to be measured.

" In operation, if the gas passing through glass I tube l contains moisture, some of its moisture is 25.

deposited on the hygroscopic glass surface, rendering it more conducting, and, by virtue oi the polarity of source B1, causing grid G1 of tube V to assume an increased positive-bias. As the res sistance of the dampened surface is decreased, the 30- positive bias of the .grid is increased, due to the increase in current in the grid-cathode space path. This immediately causes an increase in the anode current of the tube V.

Assume that initially potentiometers Re and R2,

" Ra, R4 are so adjusted that, with practically dry through the glass tube, but by using samples of gas of known moisture content the meter is readily calibrated to read directly in percentage moisture content or absolute humidity.

I claim:

2,015,125 grid Ch is tapped to an intermediate potential or large, and

directly proportional to the moisture content of the gas'passed 1. A devlceior measuring the moisture content 01' a fluent atmosphere, comprising, a pair of electrodes spaced by a singlesection of. electric y non-conducting material, impervious to moist e, said"material having a smooth, hygroscopic, con-' tinuous surface, an electronic tube having an anode, a cathode, and a grid, an electrical pathincluding a voltage source and said cathode and grid, adapted to pass between. said spaced electrodes, a current determined by moisture content of said gas, and means responsive to the anode current of said tube for indicating said moisture content. 2.'A device for measuring the moisture content of a gas, comprising, a pair of electrodes spaced by a single section of non-conducting ma- 'terial, impervious to moisture, said material having a smooth, hygroscopic, continuous surface, means inducing a continuous flow of the gas past said electrodes, an electronic tube having an anode, a cathode, and agrid, an electrical path including a voltage source and the cathode-grid space path of said tube adapted to pass between said spaced electrodes a'current determined by the moisture content of the gas, and means responsive to the anode current of said tubefor measuring said moisture content 3. A device for measuring the moisture content of a fluent'atmosphere, comprising; a glass tube, spaced electrodes embedded and housed-therein,

an electronic tube having, an anode, a cathode,

and a grid, an electrical path including a voltage source and the cathode-grid space path of saidtube adapted to pass between said spaced electrodes a current determined by said moisture content, and a meter responsive to the anode currentv of said tube for indicating said moisture content.

4. In a system for determining the moisture content of a gas, said system including a pair of electrodes spaced by a single section of non-conducting material, impervfous to moisture, said material having a smooth, hygroscopic, continuous surface, and means for impressing a voltage between said electrodes, the method of, determining 'said moisture content which comprises, in-

- ducing a continuous flow of the gas past said electrodes, and measuring variations in electrical conductivity of the path between said electrodes.

HERBERT S. POLIN.

' Disclaimer.

2,015,l25.-Herbert Spencer Polin,

ETER. Patent dated Sept. the assignee, Polin, Inc.

Port Washington, Long Island, N. Y. Hrcaon- 24, 1935. Disclaimer filed Jan. 25 1950, by

Hereby enters this disclaimer to. claim 1 of said patent.

[Ofiict'al Gazette February 21, 1 950.]

battery Ba. k

The grid leak desistance Re is very serves to prevent the grid from becoming free" or floating, i. e. it serves to prevent accumulation of free charges on the grid 6, should the electrode device Dbecome so dry as to become a substantially perfect insulator.

Cathode K is variably tapped by connection 4 to the potentiometer Ra. By proper adjustment of tap 4 to potentiometer R: as well as the-tap to potentiometer Re, the extremities 5 and 6 of the potentiometer R2, R3, R4, maybe brought to the same potential for a selected reference condition of device D, providing thereby a zero reference indication on meter M.

A ian'F or other suitable device may be'employed to induce a continuous flow of the gas through device D. 0r such flow may be obtained by mounting device D on a member, such as an airplane wing, movable with respect to the gas to be measured.

" In operation, if the gas passing through glass I tube l contains moisture, some of its moisture is 25.

deposited on the hygroscopic glass surface, rendering it more conducting, and, by virtue oi the polarity of source B1, causing grid G1 of tube V to assume an increased positive-bias. As the res sistance of the dampened surface is decreased, the 30- positive bias of the .grid is increased, due to the increase in current in the grid-cathode space path. This immediately causes an increase in the anode current of the tube V.

Assume that initially potentiometers Re and R2,

" Ra, R4 are so adjusted that, with practically dry through the glass tube, but by using samples of gas of known moisture content the meter is readily calibrated to read directly in percentage moisture content or absolute humidity.

I claim:

2,015,125 grid Ch is tapped to an intermediate potential or large, and

directly proportional to the moisture content of the gas'passed 1. A devlceior measuring the moisture content 01' a fluent atmosphere, comprising, a pair of electrodes spaced by a singlesection of. electric y non-conducting material, impervious to moist e, said"material having a smooth, hygroscopic, con-' tinuous surface, an electronic tube having an anode, a cathode, and a grid, an electrical pathincluding a voltage source and said cathode and grid, adapted to pass between. said spaced electrodes, a current determined by moisture content 10 of said gas, and means responsive to the anode current of said tube for indicating said moisture content. 2.'A device for measuring the moisture content of a gas, comprising, a pair of electrodes 16 spaced by a single section of non-conducting ma- 'terial, impervious to moisture, said material having a smooth, hygroscopic, continuous surface, means inducing a continuous flow of the gas past said electrodes, .an electronic tube having an 20 anode, a cathode, and agrid, an electrical path including a voltage source and the cathode-grid space path of said tube adapted to pass between said spaced electrodes a'current determined by the moisture content of the gas, and means responsive to the anode current of said tubefor measuring said moisture content...

3. A device for measuring the moisture content of a fluent'atmosphere, comprising; a glass tube,

spaced electrodes embedded and housed-therein, an electronic tube having, an anode, a cathode,

and a grid, an electrical path including a voltage source and the cathode-grid space path of saidtube adapted to pass between said spaced electrodes a current determined by said moisture content, and a meter responsive to the anode currentv of said tube for indicating said moisture content.

4. In a system for determining the moisture content of a gas, said system including a pair of electrodes spaced by a single section of non-con- 40 ducting material, impervious to moisture, said material having a smooth, hygroscopic, continuous surface, and means for impressing a voltage between said electrodes, the method of, determining 'said moisture content which comprises, in- 45, ducing a continuous flow of the gas past said electrodes, and measuring variations in electrical conductivity of the path between said electrodes.

HERBERT S. P011111.

Disclaimer, I 2,015,125.--Herbert Spencer Polin, Port Washington, Long Island, N. Y. Hrcaom- ETER. Patent dated Sept. the assignee, Polin, Inc.

24, 1935. -Disclairner filed Jan. 25 1950, 'by

Hereby enters this disclaimer to. claim 1 of said patent.

[Ofiict'al Gazette February 21, 1 950.] 

